Callendar has obtained some excellent diagrams from petrol
engines, of which two are given in Fig. 1005 as samples. In
addition to the diagram itself he photographed a spark on the
plate which occurred simultaneously with that in the cylinder.
The case B was when the spark was made just after compression,
and case A when (advanced' to such a position as to give fullest
fCTMOSPH LfNE. ,
value to the initial pressure. Before removing the plate the
atmospheric line must be drawn by suitably changing the tap of
the three-way cock on the engine cylinder. The manograph is
fixed upon a tripod when in use, and is placed as near as possible
to the motor, so as to shorten the pressure pipe and avoid abrupt
bends in the driving shaft.
Pp. 633 and 893. High-speed Engines.—The Belliss
engine, Fig. 1006, has been considerably and successfully used
for direct dynamo driving in light stations, and at one time
divided the honours of that class of work almost entirely with the
Willans engine, p. 893. The design of this engine is not in any
way new or striking, for it is simply of compound inverted side-
by-side typef as in marine practice, while the central distributing
piston valve is similar to that in the Westinghouse engine, G,
p. 632. Unlike the latter, the Belliss engine is double-acting,
and it is also of larger size. Its success has depended very much
on its careful build, but most particularly on the way in which
any possible 'knock' is resisted by oil under pressure. The.
shock due to the reversal of < reciprocating parts was formerly!
softened by the compression oi/ cushioning of steam at the end ©£